Printed TTI indicators

ABSTRACT

The present invention relates to time-temperature integrating indicators, also known as TTI indicators, which are easily printable on substrates, such as packaging materials, and to a method for the manufacture of packaging materials comprising printed TTI indicators. The printed TTI indicator is selectively activated at the time of packaging of a perishable product or alternatively at the time of opening of the package of a perishable product.

FIELD OF THE INVENTION

The present invention relates to time-temperature integratingindicators, also known as TTI indicators, which are easily printable onsubstrates, such as packaging materials, and to a method for themanufacture of packaging materials comprising printed TTI indicators.The printed TTI indicator is selectively activated at the time ofpackaging of a perishable product or alternatively at the time ofopening of the package of a perishable product.

STATE OF THE ART

Colour-changing or colour-forming temperature sensitive indicators formonitoring of handling of perishable goods are well known in the art.Such perishable goods are for example foodstuffs, pharmaceuticals,biological materials, chemical substances, coating compositions,adhesives, cosmetics, food additives, photographic supplies andvaccines. There is a growing interest for indicator systems and devicesfor monitoring a temperature and a time as an accumulated value ofarticles, which are stored at a constant temperature for a certainperiod of time. Particularly such indicator systems are used forsignaling when the articles have reached the point of quality loss orunsafe condition due to excessive temperature exposures.

Several time-temperature integrating indicator systems and devices havebeen proposed. Usually they are either attached as adhesive labels tothe surface of consumer packages of perishable goods or incorporatedonto the packages at the time of production of the goods to show when apackage has been temperature abused or has reached the end of its usefulshelf life. Most of the TTIs available are colourimetic labels, whichrespond to cumulative exposure to time and temperature.

TTIs typically provide a visual indicator that gradually changes withtime faster at elevated temperatures and slower at colder temperatures.Commercially available are products, which employ enzymatic colourindicators to show the amount of higher temperature exposure of a storedor shipped temperature-sensitive commodity. The enzyme indicator isactivated at the beginning of a monitoring period by applying pressureon a plastic bubble strip thus releasing the enzyme, substrate andindicator to react with each other. Another indicator system is based ona polymerisation reaction and the system must be stored frozen prior tousage. Also a product based on a dyed wax that diffuses along a strip ofpaper is known.

An improved indicator system utilising the concept of two differentindicator technologies is disclosed in EP 0 484 578. This indicatordevice comprises a system of printable multi-layer compatiblecomposition with an independently acting integrating indicator andanother threshold indicator. In a preferable embodiment, diacetylenicmonomers are printed on a transparent film as the primary indicia oflong-term storage. As a function of time and temperature, the materialgradually and irreversibly develops colour. The secondary indicator isset to trigger at a pre-determined temperature very rapidly. Thecombined indicator device yields a single output.

U.S. Pat. No. 5,756,356 discloses an indicator material and a method ofindicating a time or a temperature time accumulated value as a colourchange which comprises providing an oxidation-polymerizable dyestuff(agent A) and oxidising agent (agent B) in a non-contact state and theagent A and/or the agent B being held in a carrier which may be a resinor liquid media. When activation takes place, A and B are brought intocontact with each other. In said indicator material, between a firstlayer containing agent A in a carrier and a second layer containingagent B in a carrier, there is a third layer so-called spacing layerwhich may include woven fabric, non-woven fabric, powder andmicro-capsules. The indicator material may be obtained by a printingmethod using as a carrier a source marking ink, such as gravure ink,offset ink, screen ink, a lithographic ink or flexographic ink, or by aprinting method using an on-demand ink, such as stamp ink, carbon-freepaper ink, inkjet ink, wire dot ink, typewriter ink or thermal ink. Alayer containing the agent B may be directly formed on the surface of atape-shaped layer containing the agent A by printing method just beforeinitiation of the measurement of the temperature time accumulated value.A layer containing the agent A may be formed on a transparent substrateby a printing method and the resultant laminate may be attached to asurface over tape-shaped layer containing the agent A just before theinitiation and a measurement of a temperature-time accumulated value. Alayer containing the agent A and a layer containing the agent B may beformed on a transparent film by any one of a silk screen printingmethod, a gravure printing method and an offset printing method.However, control of the reaction rate of an oxidation reaction may causedifficulties and the colour change may not be sufficiently fast.

A recording material is provided in EP 1048477, which material issuitable for use in a direct thermal imaging apparatus and whichcontains at least one indicator compound that is convertible from aninactive state to an active state by the application of heat with adirect thermal imaging apparatus. The recording material refers to anysubstrate that is suitable for use in a thermal imaging apparatus and itmay take the form of an article or product packaging such as a cardboardcontainer or a label. Substrates may include all types of paper, boththermal paper and non-thermal paper or adhesive labels. Preferredindicator compounds are kinetic indicator compounds, which provide achange in colour from a chemical reaction in response to the exposureelement of interest such as integrated time and temperature. It may beconvenient to apply the indicator composition in the form of a printedmessage on the recording material or alternatively, the layer of theindicator compound on the recording material can be activated in theform of a printed message. This method requires always the use of athermal imaging apparatus.

WO 01/64430 discloses an indicator system, which is attached to a unitof thermally sensitive perishable product and is activated at a time ofintroduction of the unit into commerce to initiate the monitoring of theunit's cumulative exposure to harmful temperatures. Said indicatorsystem comprises use of a direct self-adhesive thermal label papercomprising a colour-forming high-temperature printing composition, and asecond activating element component in the form of a self-adhesive tabor label comprising a substrate, an adhesive composition and anactivating component that, when applied to the direct thermal coating,combines with the primary composition to enable its colour-formingreaction. The application of the second element may also be performeddirectly in fluid form using clear ink comprising an activatingcomponent.

An indicator device for use in steam sterilization is disclosed in U.S.Pat. No. 4,410,493. Said device consists of a permeable wick materialwhich is treated with a suitable indicator chemical such as sebacicacid, to provide an indication like colour change when exposed tocertain constituents in an environment. The wick is sealed between twolayers of an impermeable material and the device may contain a backingmaterial of polymeric material or metal foil.

Several activatable time-temperature indicator systems have beenproposed. Most of the systems involve a complicated indicator system ora label which is to be affixed to a perishable product and oftenco-reactant components are in close proximity but yet maintainingreactive isolation by means of additional intervening layers,encapsulating films and the like. Such TTI systems and devices are oftencostly to manufacture, complicated to activate and they are prone toinadvertent premature activation. Additionally, adhesive labels tend tobe released from the articles. Based on the above it can be realisedthat there exists a need for a low cost and reliable time-temperatureindicator, which is directly printable on the packaging material, whichcan be cost effectively manufactured and easily activated and noaffixing of labels or use of any additional equipment is required.

OBJECT OF THE INVENTION

An object of the present invention is a TTI indicator, which can bedirectly printed on a substrate material and which can be activated at adesired moment by printing, or alternatively a TTI indicator, which canbe printed between layers of a substrate material, and which can beactivated at a desired moment by opening of a package containing theindicator. Said TTI indicator provides a rapid and clear indication ofexpiration.

A further object of the invention is a method for the manufacture of TTIindicator, which can be directly printed on a substrate material andwhich can be activated at a desired moment by printing, or alternativelya TTI indicator, which can be printed between layers of a substratematerial, and which can be activated at a desired moment by opening of apackage containing the indicator, and which indicator provides a rapidand clear indication of expiration.

A further object of the invention is a method for the monitoring atemperature and a time as an accumulated value of a perishable productwith the TTI indicator according to the invention, either from the timeof packaging of the perishable product or in the alternative embodiment,from the time of opening of the package of the perishable product.

The characteristic features of the printed TTI indicator, of the methodfor the manufacture of a printed TTI indicator and of the method for themonitoring a temperature and a time as an accumulated value of aperishable product with the TTI indicator according to the invention areprovided in the claims.

SUMMARY OF THE INVENTION

It has now been realised that a TTI indicator can be easily manufactureddirectly on a substrate in connection with printing of the substrate,and suitably at the time of packaging of the final product, which is tobe monitored. Thus the time of printing is the time of activation.

In an alternative embodiment the TTI may be printed between layers of asubstrate material. At the time of packaging of the final product or atthe time of the manufacture of the packaging material/substrate the TTIindicator may be printed on the inner side of the packaging material andit is then sealed between packaging material/substrate layers. The TTIis activated at a desired moment by opening of a package, containing theindicator, of the perishable product.

The TTI indicator according to the invention comprises a substrate, anoptional protective layer on the substrate, a diffusion layer, agent Aand agent B on the substrate or on the protective layer or on thediffusion layer, and an optional outer protective layer. In the firstembodiment agent A and agent B are adjacent to each other but not indirect contact with each other. In the alternative embodiment agent Aand agent B are in direct contact with each other and either adjacent toeach other, on the top of each other or blended together.

DETAILED DESCRIPTION OF THE INVENTION

It has been noted that many of the problems and disadvantages related tothe solutions according to the prior art can be avoided or at leastsubstantially decreased by the TTI according to the invention. A TTIindicator can be easily manufactured directly on a substrate inconnection with printing of the substrate, and suitably at the time ofpackaging of the final product, which is to be monitored. The time ofprinting of the TTI indicator is the time of activation of the TTIindicator.

In the alternative embodiment the TTI may be printed between layers of asubstrate material. At the time of packaging of the final product or atthe time of the manufacture of the packaging material/substrate the TTIindicator may suitably be printed on the inner side of the packagingmaterial and it is then sealed between packaging material/substratelayers. The TTI is activated at a desired moment by opening of apackage, containing the indicator, of the perishable product.

The TTI indicator according to the first embodiment of the inventioncomprises a substrate, an optional protective layer on the substrate, adiffusion layer, at least one stripe or dot or a geometrical figurecomprising agent A and at least one stripe or dot or a geometricalfigure comprising agent B, adjacent to each other but not in directcontact with each other, on the substrate or on the protective layer oron the diffusion layer, and an optional outer protective layer.

The TTI indicator according to the alternative embodiment of theinvention comprises a substrate, an optional protective layer on thesubstrate, a diffusion layer, at least one stripe or dot or ageometrical figure comprising agent A and at least one stripe or dot ora geometrical figure comprising agent B, in direct contact with eachother and either adjacent to each other, on the top of each other orblended together, on the substrate or on the protective layer or on thediffusion layer, and an optional outer protective layer and an outersubstrate layer.

The invention is illustrated in more detail with enclosed FIGS. 1-3:

FIG. 1. A TTI indicator according to the first embodiment of theinvention with a diffusion layer C on the agents A and B.

FIG. 2. A TTI indicator according to the alternative embodiment of theinvention with a diffusion layer C on the agents A and B, which are ontop of each other.

FIG. 3. Another TTI indicator according to the alternative embodiment ofthe invention with a diffusion layer C on the agents A and B, which areblended together.

In FIG. 1 a TTI indicator according to the invention is presented.Agents A and B are printed on a substrate D (which is optionally coatedwith a protective layer) as stripes, dots or geometrical figures,adjacent to each other but not in direct contact with each other. On theagents A and B a diffusion layer C is printed, which may optionally becoated with a protective layer.

In FIG. 2 a TTI indicator according to the alternative embodiment of theinvention is presented. Agents A and B are printed on a inner substratelayer D1 (which is optionally coated with a protective layer) asstripes, dots or geometrical figures, on top of each and in directcontact with each other. On the agents A and B a diffusion layer C isprinted, which may optionally be coated with a protective layer. Theindicator is covered the outer substrate layer D2 (which is optionallycoated with a protective layer), which may comprise same or differentmaterial as the inner substrate layer D1.

In FIG. 3 another TTI indicator according to the alternative embodimentof the invention is presented. A blend of agents A and B is printed on ainner substrate layer D1 (which is optionally coated with a protectivelayer) as stripes, dots or geometrical figures. On the blended agents Aand B a diffusion layer C is printed, which may optionally be coatedwith a protective layer. The indicator is covered the outer substratelayer D2 (which is optionally coated with a protective layer), which maycomprise same or different material as the inner substrate layer D1.

According to one embodiment of the invention, on the substrate oroptionally on the protective layer, which is situated on the substrate,a diffusion layer is applied, suitably by offset, inkjet, flexo,silkscreen, gravure, folio or spray printing and a particularly suitableprinting method is a digitally controlled printing inkjet method. Thesubstrate containing the diffusion layer and optional protective layermay then be stored in a warehouse etc until the final product is packedin it. In the first embodiment, in connection with the manufacture ofthe final package containing the product the agents A and B and theoptional outer protective layer are applied by printing on the diffusionlayer and the activation of the indicator takes place.

According to another embodiment of the invention, the agents A and B,the diffusion layer and optionally the protective layer(s) are allapplied by printing on the substrate or on the protective layer inconnection with the manufacture of the final package containing theproduct and the activation of the indicator takes place. A suitableprinting method is offset, inkjet, flexo, silkscreen, gravure, folio orspray printing, preferably inkjet, and particularly preferably adigitally controlled inkjet printing method is used.

In the first embodiment the activation of the TTI indicator is performedby printing agent A and agent B in connection with packaging of goods tobe monitored. Agents A and B may be printed in the form stripes or dotsor geometrical figures, and the like. All conventional graphics,including barcodes, required for the indicator may be printedsimultaneously.

In the alternative embodiment the TTI indicator is printed between thepackaging material/substrate layers and it is activated by opening thepackage, particularly by tearing the packaging material containing theTTI indicator between the packaging material and thus revealing theindicator and exposing it to the surrounding atmosphere. The agent B ispreferable an easily evaporating organic acid in this embodiment.

In another embodiment a combination of TTI indicator and an additionaltemperature indicator is printed on the substrate/packaging.

The substrate is selected from packaging material, which may comprisepaper, cardboard, plastic foil, metal or glass, preferably paper,cardboard or plastic foil.

The substrate may optionally comprise a protective layer, which is anytransparent material with good water vapour barrier properties. Suitableones are polyolefins as well as aqueous and solvent containing laquers.Preferably polyethylene, polypropylene and acrylic based lacquers areused. The protective layer is applied onto the substrate by a suitablecoating or printing method known to a man skilled in the art, such asspray coating, laminating or offset, inkjet, flexo, silkscreen, gravure,folio or spray printing, a preferable printing method is a digitallycontrolled inkjet printing method. The protective layer may also beapplied on the TTI as an outer protective layer to prevent agents A andB from drying.

The diffusion layer is a membrane comprising film-forming substancesselected from cellulose derivatives such as carboxy methyl cellulose,micro-crystalline cellulose, methyl cellulose, hydroxypropyl methylcellulose, starches, corn protein (Zein protein), soy protein, casein,glutein, cyclodextrins, cithosan, lecithin and phospholipide, hydro-gelsand sol-gels, gum arabic, agarose and resins, dissolved in a solvent ormixture of solvents. Suitable solvents are water, alcohols such asethanol and glycols, such as polyethylene glycol.

Also additives selected from lauric acid, cinnamic aldehyde, eugenol,beeswax and acetylated monoglyseride may be used for adjusting thediffusion rate in the diffusion layer.

The thickness and density of the diffusion layer can be varied dependingof the desired diffusion rate, which corresponds to the maximum timefactor.

The indicator comprises agent A and agent B which, when brought intocontact with each other react and yield a by visual light and/orUV-light detectable change of colour. In the alternative embodiment theagent A and agent B are in direct contact with each other at the time ofactivation and the original colour of agent A returns when agent B isevaporated from the layer or mixture. This change of colour is equallydetectable by visual light and/or UV-light.

In the following table 1 suitable pH-ranges and colour changes of somesuitable pH-indicators for the present invention are disclosed.

TABLE 1 Substance Colour change Colour change pH range Thymol blueRed-yellow 1.2-2.8 Methyl orange Red-orange 3.1-4.4 Methyl redRed-yellow 4.4-6.2 Lithmus Red-blue 5.0-8.0 Bromthymol blue Yellow-blue6.0-7.6 Phenol phthalein Colourless-red 8.2-9.8 Thymol phthaleinColourless-blue  9.3-10.5

Agent A is a pH-indicator also called a pH-dye. The pH-indicator ispreferably selected from the group consisting of methyl red, cresol red,bromthymol blue, neutral red, phenol phthalein, bromocresol red,bromocresol green, bromocresol blue, xylenol blue, thymol blue, methylorange, lithmus and thymol phthalein, particularly preferablybromocresol blue. Agent A may also contain a solvent, suitably water oralcohol, such as ethanol or a mixture thereof, and/or a humectant,suitably a glycol, such as polyethylene glycol, to prevent drying of thecomposition on the print head during printing operation.

Agent B is a material with adjusted pH, preferably an organic acidselected from citric acid, tartaric acid, lactic acid, acetic acid orformic acid, preferably citric acid. Agent B may also contain a solvent,suitably water or alcohol, such as ethanol or a mixture thereof, and/ora humectant, suitably a glycol, such as polyethylene glycol, to preventdrying of the composition on the print head during printing operation.

Thus the TTI indicator according to the first embodiment is activated atthe time of packaging of the articles in the substrate material havingoptionally the printed diffusion layer on its' surface or on theprotective layer, by applying by printing the agents A and B. A suitableprinting method is inkjet, offset, flexo, silkscreen, gravure, folio orspray printing, preferably inkjet.

Agent A and agent B are preferably incorporated in a carrier, suitablyin a printing ink composition. A printing ink composition comprises:

-   -   10-20 wt-% of agent A or of agent B, or a blend thereof in the        alternative embodiment;    -   50-70 wt-% of a water-miscible or water soluble solvent, such as        an alcohol like ethanol, toluene, xylene, or mixtures thereof;    -   binder selected from oils, resins, nitrocellulose, polyamides        and acrylates; and    -   additive or combination of additives selected from plasticizers,        waxes, anti-foam substances, antioxidants, humectants and        fillers.

The printing ink composition has low viscosity, it dries rapidly and itis non-tixotropic.

According to the first embodiment of the invention one or more stripesor dots or geometrical figures comprising agents A and B may be printedon the substrate and the distance between the A and B stripes or dots orfigures can adjusted to achieve the reaction at a desired point of time.Agent A and agent B migrate in the diffusion layer towards each other.The reaction between agent A and agent B takes place at a predeterminedmoment of time and it provides a rapid and clear indication ofexpiration. The diffusion can also be influenced by the selection of asuitable pH-indicator (ph-dye) and material with adjusted pH, such as anorganic acid. Suitable printing methods are inkjet, offset, flexo,silkscreen, gravure, folio or spray printing, preferably digitallycontrollable inkjet printing methods.

The properties of the TTI indicator may be adjusted by a choice of thereactive components A and B and also by the amount of the compoundsused. The amounts may easily be adjusted by changing the gravure figuresin printing, the cell size, and the viscosity or dry/solid content ofthe printing ink.

Because the printing may be carried out just before or at the time ofpackaging of the product, this makes it possible to rapidly andspecificly for each product to change the time-temperature sensitivity.

The present invention comprises a TTI indicator which is printed on asubstrate such as cardboard or paper, useful as packaging material forperishable goods and activated by printing the indicator at the time ofpackaging and releasing of the goods on the market. Said printedindicator is useful for monitoring the exposure of a perishablefoodstuff or a commodity product to a critical condition of such timeand temperature which will result in spoilage or unacceptabledegradation of the quality of the perishable product.

In the alternative embodiment the TTI indicator is printed between thepackaging material/substrate layers and it is activated by opening thepackage, particularly by tearing the packaging material containing theTTI indicator between the packaging material and thus revealing theindicator and exposing it to the surrounding atmosphere. This embodimentis particularly suitable for monitoring of the time and temperature,which will result in spoilage or unacceptable degradation of the qualityof a perishable product after opening of the package. The easilyevaporating agent B is released from the TTI indicator, resulting in achange of colour.

Perishable products include foodstuffs such as meat, fish, poultry,plants and the like, food additives, biological materials, drugs,cosmetics, photographic supplies, coating compositions, adhesives,vaccines, implantation related organs and chemical substances.

Visible light or humidity in the surroundings has no effect on thereaction between agents A and B.

The parameters and the sensitivity of the reaction can be easilyadjusted, even during the manufacturing process. The content of theprinted information can be changed in-line during the printing process.The process according to the invention allows the production of TTIindicators, which perform in a controlled and reliable manner and whichprovide a rapid and clear indication of expiration.

The present invention provides a cost effective printed TTI indicator ona substrate or between the substrate, it is easy to use, environmentallyacceptable as the indicator is printed directly on substrate, it is notmuch labour consuming as no affixing of labels is needed. Further, asdifferent products have different temperature/time limits and expirationtimes and earlier several different types of indicator labels wereneeded, the present invention provides a method which yields indicatorsfor different products by adjusting in-line the amounts of eachcomponent, the distances of stripes or dots or figures of agents A andB, by using a digitally controllable printing method for the printing ofthe ingredients of the indicator. The components are also suitable forthe use in food products.

1. A TTI indicator device comprising: a substrate layer selected frompackaging materials comprising paper, cardboard, plastic foil, metal orglass; agent A and agent B, a diffusion layer comprising film-formingsubstance(s) selected from carboxymethyl cellulose, micro-crystallinecellulose, methyl cellulose, hydroxypropylmethyl cellulose, starches,corn protein, soy protein, casein, glutein, cyclodextrins, cithosan,lecithin, phospholipide, hydro-gels, sol-gels, gum Arabic and agarosedissolved in a solvent or mixture of solvents, agent A being apH-indicator and agent B being an organic acid selected from citricacid, tartaric acid, lactic acid, acetic acid and formic acid, and a)the agent A and agent B being adjacent to each other but not in directcontact with each other and the diffusion layer being on the agent A andagent B, or b) the agent A being on top of agent B and the diffusionlayer being on the agent A, or the agent B being on top of the agent Aand the diffusion layer being on the agent B; or c) a blend of theagents A and B being on the substrate layer and the diffusion layerbeing on the blend.
 2. The TTI indicator device according to claim 1,wherein the substrate layer comprises a protective layer and the agent Aand agent B being on the protective layer.
 3. The TTI indicator deviceaccording to claim 1, wherein the diffusion layer comprises a protectivelayer thereon.
 4. The TTI indicator device according to claim 1, whereinin alternatives b) and c) the TTI indicator comprises an outer substratelayer on the diffusion layer.
 5. The TTI indicator device according toclaim 4, wherein the TTI indicator is activatable at a desired moment byopening of a package containing the indicator.
 6. The TTI indicatordevice according to claim 4, wherein the TTI indicator comprises aprotective layer on the outer substrate layer.
 7. The TTI indicatordevice according to claim 1, wherein the TTI indicator is activatable ata desired moment by printing of the indicator.
 8. The TTI indicatordevice according to claim 1, wherein the protective layer is selectedfrom polyolefins and lacquers, preferably the protective layer comprisespolyethylene, polypropylene or acrylic based lacquer.
 9. The TTIindicator device according to claim 1, wherein the solvents are selectedfrom water, alcohols and glycols.
 10. The TTI indicator device accordingto claim 1, wherein the agent A is selected from the group consisting ofmethyl red, cresol red, bromthymol blue, neutral red, phenol phthalein,bromocresol red, bromocresol green, bromocresol blue, xylenol blue,thymol blue, methyl orange, lithmus and thymol phthalein, preferablybromocresol blue.
 11. The TTI indicator device according to claim 1,wherein the agent A contains a solvent or a mixture thereof and/or ahumectant.
 12. The TTI indicator device according to claim 1, whereinthe agent B contains a solvent or a mixture thereof and/or a humectant.13. A method of monitoring the exposure of a perishable product to acritical condition of such time and temperature which will result inspoilage or unacceptable degradation of the quality of the perishableproduct using the TTI indicator according to claim
 1. 14. The monitoringmethod according to claim 13, wherein the perishable products includefoodstuffs, food additives, biological materials, drugs, cosmetics,photographic supplies, coating compositions, adhesives, vaccines,implantation related organs and chemical substances.
 15. A method forthe manufacture of a TTI indicator device, wherein at least one stripeor dot or a geometrical figure comprising agent A and at least onestripe or dot or a geometrical figure comprising agent B are printed ona substrate layer, whereon either or both agent A and agent B adiffusion layer is provided, the diffusion layer being printed, thesubstrate layer being selected from packaging materials comprisingpaper, cardboard, plastic foil, metal or glass, the diffusion layercomprising film-forming substance(s) selected from carboxymethylcellulose, micro-crystalline cellulose, methyl cellulose,hydroxypropylmethyl cellulose, starches, corn protein, soy protein,casein, glutein, cyclodextrins, cithosan, lecithin, phospholipide,hydro-gels, sol-gels, gum Arabic and agarose, dissolved in a solvent ormixture of solvents, the agent A being pH-indicator and the agent Bbeing an organic acid selected from citric acid, tartaric acid, lacticacid, acetic acid and formic acid; and the at least one stripe or dot ora geometrical figure comprising the agent A and the at least one stripeor dot or a geometrical figure comprising the agent B are printedadjacent to each other but not in direct contact with each other; or atleast one stripe or dot or a geometrical figure comprising the agent Aand at least one stripe or dot or a geometrical figure comprising theagent B, one of either agent A or agent B being arranged on top of theother, are printed on top of each other on the substrate layer; or atleast one stripe or dot or a geometrical figure comprising a blend ofthe agent A and the agent B is printed on the substrate layer.
 16. Themethod according to claim 15 for the manufacture of a TTI indicatordevice, wherein a protective layer is printed on the substrate layer andthe agent A and the agent B, one of either agent A or agent B beingarranged on top of the other, are printed on the substrate comprisingthe protective layer.
 17. The method according to claim 15 for themanufacture of a TTI indicator device, wherein a protective layer isprinted on the diffusion layer.
 18. The method according to claim 17 forthe manufacture of a TTI indicator device, wherein the diffusion layeror diffusion layer printed with the protective layer is covered with anouter surface layer.
 19. The method according to claim 18 for themanufacture of a TTI indicator device, wherein on the outer surfacelayer a protective layer is printed.
 20. The method according to claim15 for the manufacture of a TTI indicator device, wherein inkjet,offset, flexo, silkscreen, gravure, folio or spray printing is used forprinting.
 21. The method according to claim 15 for the manufacture of aTTI indicator device, wherein the protective layer is selected frompolyolefins and lacquers, preferably the protective layer comprisespolyethylene, polypropylene or acrylic based lacquer.
 22. The methodaccording to claim 15 for the manufacture of a TTI indicator device,wherein the solvents are selected from water, alcohols and glycols. 23.The method according to claim 15 for the manufacture of a TTI indicatordevice, wherein the agent A is selected from the group consisting ofmethyl red, cresol red, bromthymol blue, neutral red, phenol phthalein,bromocresol red, bromocresol green, bromocresol blue, xylenol blue,thymol blue, methyl orange, lithmus and thymol phthalein, preferablybromocresol blue.
 24. The method according to claim 15 for themanufacture of a TTI indicator device, wherein the agent A contains asolvent or a mixture thereof and/or a humectant.
 25. The methodaccording to claim 15 for the manufacture of a TTI indicator device,wherein the agent B contains solvent or a mixture thereof and/or ahumectant.
 26. The method according to claim 15 for the manufacture of aTTI indicator device, wherein the agent A and the agent B areincorporated each or the agent A and the agent B as a blend, in acarrier, preferably in a printing ink composition.
 27. The methodaccording to claim 26 for the manufacture of a TTI indicator device,wherein the printing ink composition comprises: 10-20 wt-% of the agentA or the agent B or a blend thereof; 50-70 wt-% of the water-miscible orwater-soluble solvent or mixtures thereof; a binder selected from oils,resins, nitrocellulose, polyamides and acrylates; and an addictive orcombination of addictives selected from plasticizers, waxes, anti-foamsubstances, antioxidants humectants and fillers.